The present invention relates to processing substrates in a vacuum chamber. More particularly, the field of the invention is sputter coating of semiconductor wafers, and apparatus for effecting such metallization coating of wafers individually, and on a serial, continuous basis. The invention is an improvement in the arrangement for rotating the transfer plate which carries the wafers from station to station within the sputtering apparatus.
In such a continuous system, a wafer is introduced through the load lock and mounted in a transfer plate. The load lock is then pumped and the transfer plate is then rotated to move the wafer to a work station. While processing of the wafer is being conducted at the work station, a finished wafer is being unloaded at the load lock and a new wafer loaded. There may be many similar or different work stations within the apparatus. In order to provide gas tight seals, it is necessary for the transfer plate and a pressure plate behind the transfer plate to move along the axis of rotation. To form a seal cooperating with suitably placed O-rings, the pressure plate forces the transfer plate against the front wall of the vacuum chamber. To permit rotation of the transfer plate, the pressure plate moves away from the transfer plate and the transfer plate moves away from the front wall. Thus, there are two types of motion within the apparatus. First, there is a rotation of the transfer plate through a precise angle. Second, there is a motion of the plates along the axis. The two motions must be coordinated.
In the prior art, the rotation is accomplished by a chain drive and hub system coupled to a motor. The chain drive is bulky and cumbersome. The rotational axis necessitates dynamic O-ring seals which can cause vacuum leakage problems. The axial motion is mechanically independent, but synchronized by the controlling computer.
The vacuum chamber of the wafer coating system is a large cylinder. The end walls are subject to considerable pressure which necessitates means for reinforcing the end walls. In the prior art, ribs were welded on these walls. The welding of the ribs causes problems of warping of the end walls.